Post on 23-Aug-2020
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Condition Assessment of Structures(Visual inspection & non-destructive testing of structures)
16.09.2015
Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
2Course outline
IntrinsicExtrinsic
ChemicalPhysicalBiological
Initiating
Leads to
Assessed
Visual inspectionNon-Destructive TestingDestructive Testing
CrackingScaling
SpallingPopouts
Delaminationetc.
Principles forrepair and protection
DeteriorationProcess
VisibleDamage
Conditionsurvey
Repair
Factors CausingDeterioration
Conditionevaluation
Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
3
Outlines
• Main objective of condition assessment
• Deterioration / Building materials
• Condition assessment
– Condition Survey Planning
– Visual inspection
– Non-Destructive testing (NDT)
• detection of cracks/ voids/ delamination etc.
• corrosion assessment, location and diameter ofreinforcement and cover thickness
• strength estimation of concrete --- to be continued in the next lecture ---
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Main objective of condition assessment
Main objective of condition assessmentare to place the building into one of thefollowing three categories:
i. The building has not shown anysigns of distress and It satisfiesall the safety and serviceabilityrequirements according torelevant Codes of practice, henceno action is needed towardsrepairing.
ii. The building is seen to bedeficient (or distressed) but it canbe repaired and strengthened tosatisfy the Codal safetyrequirements or performancecriteria set by the user.
iii. The building is badly damaged. Itis to be demolished and a newbuilding may be built, build backbetter.
Main steps of condition assessmentwill bea) To record the damage if any, and find
out the causes for distressb) To assess the extent of distress and
to estimate the residual strengths ofstructural components and thesystem including the foundation
c) To plan the rehabilitation andretrofitting/strengthening of thebuilding
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Deterioration / Building materials (1/2)
http://www.vtt.fi/inf/pdf/technology/2012/T33.pdf
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
http://www.vtt.fi/inf/pdf/technology/2012/T33.pdf
Deterioration / Building materials (2/2)
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Condition assessment planning
Preliminary investigation:1. Review of relevant
documents2. Visual inspection, with
documentation of defects3. Field and laboratory testing4. Preliminary analysis and
evaluation
Is furtherinvestigation
required?
Detailed investigation:1. Review of additional
documents and data source2. Additional field
observations, and field andlaboratory testing
3. Detailed analysis andevaluation
YES
NO
Isrepairingrequired?
YES
NO
Identify and analysis repairoptions
Identify special conditionsto further considered (e.g.maintenance, planning
Finalreport
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Review of plans and relevant documents
• To review documents from designand construction process as well asinspection and maintenance reportsis in general the easiest way ofgathering data about the structure tobe assessed.
• It has to be assured that the revieweddocuments are correct.
• Loads can be usually determined fromcurrent loading codes andenvironmental conditions may beobtained from inspection reports.
• Resistance properties like materialand structural properties anddimension can be obtained from:– Construction specifications -
Codes– As-built drawings--architectural,
structural, mechanical, andfoundation plans
– Construction documents (e.g.material delivery documentation)
– Documentation of performance,defects, maintenance, andchanges (Alterations)
– Reports of earlier inspection andmaintenance.
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
VISUAL INSPECTION
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Scope of Visual Inspection
• Prior to the starting of visual inspection,the structural engineer is to obtain a setof the building’s structural layout plansfrom the building owner.
• The availability of the structural layoutplan will help the structural engineer to:
a) understand the structural system andlayout of the building;
b) identify critical areas for inspection;c) identify the allowable imposed loads,
in order to assess the usage andpossibility of overloading; and
d) verify if unauthorised addition oralteration works that affect thestructure of the building have beencarried out.
http://www.bca.gov.sg/PeriodicStructuralInspection/others/PSI_PE.pdf
Fig. Lahdensivu, J.
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Visual Inspection Tools and Instruments
• Simple tools and Instruments like:– Camera– Magnifying glass– Binocular– Gauge for crack width
measurement– Chisel and hammer are usually
needed.– Pocket knife, screwdriver– Occasionally, a ladder or light
platform/scaffold tower can beused for access to advantage.
http://www.bca.gov.sg/PeriodicStructuralInspection/others/PSI_PE.pdf
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Scope of Visual Inspection
http://www.bca.gov.sg/PeriodicStructuralInspection/others/PSI_PE.pdf
A visual inspection is generally carriedout of:a) the condition of the structure of
the building§ to identify the types of structural
defects§ to identify any signs of structural
distress and deformation§ to identify any signs of material
deteriorationb) the loading on the structure of the
building§ to identify any deviation from
intended use, misuse and abusewhich can result in overloading
c) any addition or alteration worksaffecting the structure of thebuilding§ - to identify any addition or
alteration works which can result inoverloading or adverse effects onthe structure
• If there are no signs of any structuraldeterioration or defects, the visualinspection should suffice and unlessthe structural engineer otherwiseadvises, no further action needs tobe taken
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Visual inspection report (example)
http://www.bca.gov.sg/PeriodicStructuralInspection/others/PSI_PE.pdf
1. General Information of the Building• address, usage of the building,
maintenance history etc.
2. Structural System of the Building• reinforced concrete, prestressed
concrete, steel, etc
3. Date and Scope of the Inspection4. Survey of addition or alteration works
to building structure5. Survey of signs of structural defects,
damages, distress, etc.6. Survey of exposure to aggressive
environment7. Conclusions on the structural
condition8. Sketches, plans and photographs
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Examples of typical defects found by visual inspection
Erosion of Brick Face Efflorescence Brick Spalling/Delaminating
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Examples of typical defects found by visual inspection
http://www-pub.iaea.org/mtcd/publications/pdf/tcs-17_web.pdf
Concrete CrackCrack and Spall of
Concrete Around SteelMember
DelaminatingConcrete
Over Reinforcement
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Non-Destructive testing (NDT)on
reinforced concrete structure
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
NDT Objectives
NDT methods are extremely valuable inassessing the condition of structures,such as bridges, buildings, elevatedservice reservoirs and highways etc.• The principal objectives of the NDT /
PDT of concrete in situ is to assess oneor more of the following properties:– In situ strength properties– Durability– Density– Moisture content– Elastic properties– Extent of visible cracks– Thickness of structural members
having only one face exposed
– Position and condition of steelreinforcement
– Concrete cover over thereinforcement.
– Reliable assessment of theintegrity or detection of defects ofconcrete members even when theyare accessible only from a singlesurface.
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
NDT Advantages and Disadvantages
Advantages
• Access to hidden items – “seethrough walls”
• Better investigations with NDT• Rapid accumulation of data• Generally less expensive than
destructive testing• Minimize interruption of building
services• Evaluation and quality assurance
Disadvantages
• More than one test method may berequired
• Environmental conditions mayeffect ordistort results
• Construction details & buildingcomponents may effect results
• Some conditions cannot bedetermined witha reasonable degree of accuracywithout destructive testing
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Typical situations where non-destructive testing is needed
• Quality control of pre-cast units orconstruction in situ
• Monitoring of strength development inrelation to load application or similarpurpose
• Location and determination of theextent of cracks, voids, honeycombingand similar defects within a concretestructure
• Determining the concrete uniformity,possibly preliminary to core cutting,load testing or other more expensive ordisruptive tests
• Determining the position, quantity orcondition of reinforcement
• Increasing the confidence level of asmaller number of destructive tests
• Determining the extent of concretevariability in order to help in theselection of sample locationsrepresentative of the quality to beassessed
• Confirming or locating suspecteddeterioration of concrete resulting fromsuch factors as overloading, fatigue,external or internal chemical attack orchange, fire, explosion, environmentaleffects
• Assessing the potential durability of theconcrete
• Providing information for any proposedchange of use of a structure forinsurance or for change of ownership.
http://www-pub.iaea.org/mtcd/publications/pdf/tcs-17_web.pdf
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
NDT Methods for Specific Distresses
Distresses Condition Assessment Methods
Air Pockets andHoneycombing
Chain Dragging, Ground Penetrating Radar, HammerSounding, Impact-Echo, Ultrasonic, Visual Inspection
Alkali-Silica Reaction Visual InspectionChloride-InducedCorrosion Half-Cell Potential, Rapid Chloride Permeability, Resistivity
Cracking Impact-Echo, Ultrasonics, Visual Inspection
DelaminationChain Dragging, Coring, Ground Penetrating Radar,Hammer Sounding, Impact-Echo, Infrared Thermography,Ultrasonics
Popouts Visual InspectionPotholing (Caving) Visual InspectionScaling Visual InspectionSpalling Visual Inspection
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
NDT for detection of cracks/ voids/delamination etc.• Hammer sounding• Chain dragging• Ground penetrating radar• Impact-echo• Ultrasonic pulse velocity• Radiographic testing• Crack width measurement
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
NDT - Sounding
• A qualitative evaluation of concrete canbe easily obtained by just sounding it(i.e. tapping it) with a hammer.
• When the hammer is struck on goodconcrete, a ringing sound is created.
• On areas where delaminations orcracks occur, the striking of thehammer produces a drum-like sound.
• The limitation of this method is that itcannot detect defects that exist deep inthe member.
• Also, defects lying under overlays arealso difficult to find.
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
NDT - Chain Dragging
• The objective is to detect regions wherethe sound from dragging the chainchanges from a clear ringing sound(sound deck) to a somewhat mute andhollow sound (delaminated deck).
• Chain drag is a relatively fast methodfor determining the location of adelamination
• Chain Dragging is normally used onlarge concrete surface areas, such asbridge decks
• The method typically rely on theexperience of the inspector todifferentiate the relative sounds ofsimilar materials
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
NDT - Ground Penetrating Radar (GPR) [1/4]
• RADAR Radio Detection andRanging.– Detect target in free space– Determine the range
• Ground-penetrating radar (GPR) isa geophysical method that usesradar pulses to image thesubsurface.
• GPR finding and detecting buriedobject.
• GPR can be used in a variety ofmedia, including rock, soil, ice,fresh water, pavements andstructures.
• Civil engineering applications– Probing into soil to detect pipelines
and tanks– Cavities– Thickness determination– Locating reinforcement– Identifying deterioration– detect objects, changes in
material, and voids and cracks
http://www.foundationperformance.org/pastpresentations/gehrig_paper_march2004.pdf
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
NDT - Ground Penetrating Radar (GPR) [2/4]
Components of GPR:• Transmitting and receiving unit• Control unit• Display unit• Power supplies
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
NDT - Ground Penetrating Radar (GPR) [3/4]
• An EM pulse is sent through an antenna,penetrating into the surveyed material.
• A portion of the energy is reflected back tothe antenna when an interface betweenmaterials of dissimilar dielectric constant isencountered.
• The amount of reflected energy at aninterface is governed by:
• where1,2 is the reflection coefficient
r1 and r2 are the dielectric constants.
21
212,1
rr
rr
eeee
r+
-=
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
• The thickness of a layer is given by:
• where– di is the thickness of layer i,– ti the total travel time through that
layer,– C is the speed of light
r,i the dielectric constant of thelayer
Typical Dielectric Constants:
ir
ii
Ctd
,2 e=
NDT - Ground Penetrating Radar (GPR) [4/4]
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
NDT - Impact-echo [1/3]
P
S
RR
Impact• Based upon evaluation of stress wavesgenerated by an elastic impact on aconcrete surface
• Originally developed at CornellUniversity and NIST by M.Sansalone and N. Carino
• Impact Echo can be used to measurethe thickness of slabs, plates, columnsand beams, and hollow cylinders.
• It can also be used to determine thelocation and extent of flaws such ascracks, delaminations, voids,honeycombing and debonding in plain,reinforced and post-tensioned concretestructures.
P – Compression wavesS - Shear wavesR - Rayleigh waves
By: Guy Rapaport, Ramboll
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Procedure• Impact Echo testing consists of
measuring both the time record andfrequency spectrum associated with amechanical impact on the surface of astructure.
• As stress waves propagate through thestructure, they reflect off internal andexternal boundaries and causeperiodic displacements on the surface.
• These motions are monitored by atransducer and digitized.
• The waveform is transformed into thefrequency domain, so that theperiodicity of stress-wave arrivals canbe accurately determined.
• As part of Impact Echo testing, directmeasurements of compression (P-)wave velocity are also made.
• Given the P-wave velocity and thearrival period (or frequency), the depthsto internal flaws or external boundariesare calculated.
NDT - Impact-echo [2/3]
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
The fundamental equation of impact-echo is d = Vp/(2f),where
d is the depth from which the stress waves are reflected (the depth of a flawor the thickness of a solid structure),
Vp is the wave speed,f is the dominant frequency of the signal
NDT - Impact-echo [3/3]
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Ultrasonic Pulse Velocity
• Ultrasonic waves are verysimilar to light waves in thatthey can be reflected,refracted, and focused.
• Reflection and refractionoccurs when sound wavesinteract with interfaces ofdiffering acoustic properties.
• Ultrasonic reflections from thepresence of discontinuities orgeometric features enablesdetection and location.
http://www.theconcreteportal.com/nde.html
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Ultrasonic pulse velocity in concrete (UPV) ASTM C597
• In the UPV method, the velocity of apulse traveling through concrete ismeasured and correlated to its stiffness
• The velocity of the pulse increases withthe stiffness of the concrete, butdecrease with increasing density.
• Wave attenuation increases whenconcrete becomes denser, because ofabsorption of energy.
• the UPV can be used in three modes –direct, semi-direct, and indirect.
• The direct mode, or the through-transmission mode, is the most reliable,but needs access to both sides of thematerial.
http://www.olsoninstruments.com/pdf_downloads/catOI_upv.pdfhttp://www.theconcreteportal.com/nde.html
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Ultrasonic pulse velocity in concrete (UPV) ASTM C597
http://www.olsoninstruments.com/pdf_downloads/catOI_upv.pdfhttp://www.theconcreteportal.com/nde.html
• The pulse velocity can be determinedfrom the following equation.
=where
V = pulse velocity (km/s),L = path length (cm),T = transit time(µs).
• Based on this technique, the velocity ofsound in a concrete is related to theconcrete modulus of elasticity.
( )
where,E = modulus of elasticity,r =density of the concrete
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Ultrasonic pulse velocity in concrete (UPV) ASTM C597
http://www.olsoninstruments.com/pdf_downloads/catOI_upv.pdfhttp://www.theconcreteportal.com/nde.html
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Radiographic testing
• Radiography can be used to obtainpermanent image of surface and sub-surface (embedded) discontinuities
• The same discontinuities can beradiographed again after a period ofservice life and the radiographs can becompared to measure the change inthe size and shape of the discontinuity.
• Radiographic testing of the structuralreinforcement in reinforced concreteelements is carried out with the use ofan apparatus containing sources ofgamma or X rays.
• The classical inspection arrangementconsists of a radiation source at oneside of the object to inspect and an X-ray film at the other side.
• There exist also radiation methods forone-side inspections, using thebackscatter effect.
• These methods need long inspectiontimes and are limited to single layers ofreinforcement near the surface.
http://www.ndt.net/article/ndtce03/papers/v020/v020.htm
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Radiographic testing
• The selection of the sourcedepends on the wall thickness,which shall be inspected
http://www.ndt.net/article/ndtce03/papers/v020/v020.htm
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Radiographic testing
• Stereo radiography is used forquantitative measurement of depth anddiameters of steel reinforcements.
• It needs two different source positions.• The reconstruction can be done by a
graphical back projection or acomputerised one.
• The simple graphical backprojection issufficient for so called simplestructures.
• This is usually some separated steelparts or one layer of steel bars.
http://www.ndt.net/article/ndtce03/papers/v020/v020.htm
Principle of stereo radiography
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Radiographic testing
Results• flat bar in the corner
pillar is shifted vertical• flat bars are led around
round bar runningvertical for the anchor
Radiation technique arrangement of the measuring point
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Crack Width Gauge• Align the Crack Width Gauge where the
calibration and the crack are the samewidth.
• Record the width, length and location ofthe crack.
Crack width measurement
Measuring Magnifier• Crack widths are normally limited to 0.2
mm or 0.3 mm in concrete structures.• Measuring Magnifier device enables
accurate determination of whethercracks exceed this limit.– Magnification 10x– Measuring range 20 mm x 0.1 mm– Field of View 32mm
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Crack width measurement
CRACK DETECTION MICROSCOPE• Measure crack widths in concrete.• Consisting of a high definition
Microscope connected to an adjustablelight source which provides a well-illuminated image under all workingconditions.
• The image is focused by turning theknob on the side of the microscope andthe eyepiece can be rotated through360 degrees to align with the directionof the crack being examined.
• The 4mm measurement has a lowerscale divided into 0.2mm divisions.
• the maximum crack widths should notexceed 0.3mm which is 15 divisions onthe scale for most types ofenvironment.
• Specification:– Magnification x 40– Measuring Range 4 mm– Divisions 0.02mm
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
NDT for corrosion assessment, location anddiameter of reinforcement and cover
thickness
• Cover meter• Half Cell Potential test• Concrete Resistivity test
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Cover meter test
• Cover meter test is used to assess thelocation and estimate the diameter ofreinforcement bars and concrete cover.
• Principle:– based measurement of change of
an elctromagnetic field caused bysteel embedded in the concrete.
• Equipment:– profometer comprise a search
head, meter and interconnectingcable.
• The concrete surface is scanned, withthe search head kept in contact with itwhile the meter indicates, by analogueor digital means, the proximity ofreinforcement
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Cover meter test
• The cover meter applies a currentpulse
• The instrument measures theamplitude of the induced current, whichdepends on the orientation, depth, andsize of the bar.
• The search head is directional andmaximum signal is obtained when thebar is aligned with the long axis of thesearch head.
• The pulse-induction technique isuniquely stable, is not affected bymoisture in concrete or magneticaggregates, and is immune totemperature variations and electricalinterference.
Cover Master, Germann Instruments:http://germann.org/products-by-application/half-cell-potential/covermaster
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Example of the cover meter test results
http://www.proceq.com/fileadmin/documents/proceq/products/Concrete/Profometer_5_/English/Proceq_Brochure_Profometer_5__E.pdf
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Half-Cell Potential Method (ASTM C 876-91)
• Then generally readings taken areat grid of 1 x 1 m for slabs, wallsand at 0.5 m c/c for Column,beams
Principle:• The electrical activity of the steel
reinforcement and the concrete leadsthem to be considered as one half ofweak battery cell with the steel actingas one electrode and the concrete asthe electrolyte.
• The electrical potential of a point on thesurface of steel reinforcing bar can bemeasured comparing its potential withthat of copper - copper sulphatereference electrode on the surface.
• Practically this achieved by connectinga wire from one terminal of a voltmeterto the reinforcement and another wireto the copper sulphate referenceelectrode.
http://theconstructor.org/concrete/corrosion-potential-assessment/2969/
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Half-Cell Potential Method (ASTM C 876-91)
The results affected by:• Degree of humidity in concrete
– More negative potentials result forconcrete with higher degree ofsaturation.
• Stray currents– The presence of stray currents will
significantly affect themeasurements of the half-cellpotential.
• Oxygen content near thereinforcement– The lack of oxygen near the
reinforcement results in morenegative potentials
• Microcracks– Localized corrosion can be
generated by microcracks, whichalso modify the concrete resistivity,consequently affecting thecorrosion potential measurement
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Example of the Half Cell Potential test result
MeasuredPotential
Ecorr values Corrosion Condition
mV vs. SCE<-426 <-500 Severe corrosion
<-276 <-350 High (>-90% risk ofcorrosion)
-126to
-275
-350to
-200
Intermediate corrosionrisk
>-125 >-200 Low (10% risk ofcorrosion)
CSE = Copper / Copper sulphate electrode,i.e. the potential values are stated with therespect to CSE
http://theconstructor.org/concrete/corrosion-potential-assessment/2969/
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Example of the Half Cell Potential test result
http://www.pcte.com.au/corromap-half-cell-potential-corrosion-rate-and-resistance-mapping
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
• The Galvanostatic PulseMeasurements technique (GPM) wasfirst used in the field in 1988.
• It provides a solution to interpretationproblems found when the half cellpotential methods is used in someenvironments, e.g. in wet concrete.
• estimation of corrosion rate as well,which means how much reinforcementsteel is being dissolved per year.
• The GalvaPulse™ is a rapid, non-destructive polarization technique forthe evaluation of reinforcementcorrosion rate as well as half-cellpotentials.
typically been used in connection with:– Swimming pools– Bridges– Balconies– Parking houses
Galvapulse - Surface Corrosion Rate System
http://www.pcte.com.au/galvapulse-surface-corrosion-rate-system
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Advantages• Estimation of the corrosion rate in the
reinforcement can be made in less than10 seconds.
• Reliable evaluation of reinforcementcorrosion also in wet, carbonated orinhibitor treated concrete.
• Half cell potential and electricalresistance of the cover layer are given.
• Lightweight electrode / hand heldcomputer and easy to operatesoftware.
• Durable Guard Ring system forfocusing the current field to thereinforcement.
• Measurements possible on uneven andcurved surfaces.
• Measurement results in Excel-formatare easily transferred to PC for furtherprocessing and presentation.
Threshold values
Galvapulse - Surface Corrosion Rate System
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Concrete Resistivity test
The Measurement Principle• measure the electrical resistivity of
concrete or rock in a non-destructivetest.
• A current is applied to the two outerprobes, with the difference measuredby the two inner probes.
• In concrete material with high electricalresistivity the corrosion process will beslow compared to concrete with lowresistivity in which the current caneasily pass between anode andcathode areas
http://www.rbmltd.co.il/img/ckFiles/files/ProductsPDF/Proceq/resipod_SF_E_2013_06_19_low.pdf
Wherea is probe spacing [cm]V is measured potential [V]I is the current applied [A]
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Concrete Resistivity test result
http://www.electrochemsci.org/papers/vol2/2010001.pdf
• The electrical resistivity of concrete wasproposed as an effective parameter toevaluate the risk of reinforcing steelcorrosion, particularly when corrosion isinduced by chloride attack
• The resistivity measurement is a usefuladditional measurement to aid inidentifying problem areas or confirmingconcerns about poor quality concrete.
• Measurements can only be consideredalong side other measurements.
• Reinforcing bars will interfere withresistivity measurements.
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Limitation• It is difficult to measure resistivity in
very close reinforcement• Carbonation may affect the
resistivity• It cannot be used where ambient
change in temperature is there.• Experience operator is required to
handle this equipment.
Concrete Resistivity test
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Summary
Lecture summary
• Main objective of condition assessment
• Deterioration / Building materials
• Methodology of condition assessment
– Condition Survey Planning
– Visual inspection
– Non-Destructive testing (NDT)
• detection of cracks/ voids/delamination etc.
• corrosion assessment,location and diameter ofreinforcement and coverthickness
Next lecture– Tests for strength estimation of
concrete– Destructive and laboratory
testing on reinforced concretestructure
– Mold inspection– Inspection of masonry walls– Inspection of rendered facades